style: fix missing space

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/complex/base/cast-return/examples/index.js

@@ -27,7 +27,7 @@ var f = castReturn( addf, 2, Complex64 );
 // ...
 
 var z = f( 3.0, 4.0 );
-// returns <Complex64>[ 7.0, 0.0]
+// returns <Complex64>[ 7.0, 0.0 ]
 
 
 console.log( z.toString() );